1. Field of the Invention
The invention relates to a magnetic modulator circuit for providing a pulse to a load.
2. Description of the Prior Art
It has long been known that some magnetic materials have a characteristic saturation point at which their magnetic permeability changes rapidly as the applied magnetic field increases. Magnetic modulators or switches have been developed to make use of this characteristic. Typically, these magnetic modulators include a closed magnetic circuit or magnetic core, sometimes called a saturable reactor. A field is applied to the magnetic core by a primary coil, inducing a voltage across a secondary coil around the magnetic core. The secondary coil is connected to a pulse forming network which is essentially capacitive. As a result, when the magnetic core saturates, so that the impedance across the secondary coil drops, the pulse forming network discharges through the load.
An important advantage of magnetic modulators or switches is reliability. Since the switching action is provided by the magnetic core itself, no high voltage switch such as a spark gap or a thyratron is necessary. These high voltage switches wear out or erode over a period of usage, but the magnetic core does not wear out. It may become magnetized, but this condition can be reversed by an appropriate resetting coil.
As noted above, the typical magnetic modulator includes a pulse forming network which compresses the voltage induced in the secondary coil to provide a pulse to a load. The known pulse forming networks are separate components from the magnetic core. Typically, a pulse forming network includes one or more lumped components, such as capacitors. It is sometimes necessary to improve the flatness of the pulse top and to shorten the rise time for short pulses. This can be done by using a distributed pulse forming line such as a length of coaxial cable.
It would be advantageous to provide a distributed pulse forming network for a magnetic modulator or switching circuit which flattens the pulse top and shortens the rise time, but which does not require any additional components. Such an arrangement would reduce the size of the magnetic modulator, would improve the pulse shape, and would also provide the long life characteristic of magnetic modulators. It would further be desirable to provide a magnetic modulator with a distributed pulse forming network having an impedance which could be varied easily by modifying its parameters. In particular, a distributed pulse forming network having a high impedance is sometimes desirable, and is difficult to obtain using coaxial cable.